1. Field of the Invention
The present invention relates to a process cartridge and an image forming system on which such the process cartridge can be mounted. Such an image forming system may be embodied, for example, as an electrophotographic copying machine, a laser beam printer, a facsimile, a word processor or the like.
2. Description of the Related Art
In image forming systems such as copying machines, a latent image is formed by selectively exposing an image bearing member uniformly charged, the latent image is then visualized with toner, and then the toner image is transferred onto a recording sheet, thereby forming an image on the recording sheets. In such image forming systems, whenever the toner is used up, new toner must be replenished. The toner replenishing operation not only is troublesome, but also often causes the contamination of the surroundings. Further, since the maintenance of various elements or members can be performed only by an expert in the art, most of the users feel inconvenient.
In order to eliminate such drawbacks and inconvenience, an image forming system wherein parts such as a developing device in which toner was used up or an image bearing member of which a service life was expired can easily be exchanged, thereby facilitating the maintenance, by assembling the image bearing member, a charger, the developing device and a cleaning device integrally as a process cartridge which can be removably mounted within the image forming system has been proposed and put into practical use, for example, as disclosed U.S. Pat. Nos. 3,985,436, 4,500,195, 4,540,268 and 4,627,701.
A conventional process cartridge is formed by a first unit holding a photosensitive drum, and a second unit holding a developing sleeve. In the first unit, the photosensitive drum is provided at both of its ends with flange gears and is supported by a frame of the first unit via drum shafts passing through holes formed in the flange gears. On the other hand, in the second unit, within the developing sleeve, there is disposed a magnet for holding magnetic developer on a surface of the developing sleeve. The developing sleeve is supported and fixedly held by a bearing mounted on a frame of the second unit via a flange secured to one end of the developing sleeve.
Further, the magnet is provided at both of its ends with D-cut portions. One end of the magnet at a driving side of the developing sleeve passes through the interior of the flange and is fixedly held by the frame of the second unit via a bearing and the other end of the magnet is also fixedly held by the frame of the second unit via a bearing.
Incidentally, the first and second units are held in a confronting relation to each other by springs and the like so that a predetermined distance is maintained between the photosensitive drum and the developing sleeve.
However, with the above-mentioned arrangement, a distance between the photosensitive drum and the magnet is varied or changed during the image forming operation due to the eccentricity or deflection of the developing sleeve, the poor concentricity between the developing sleeve and its flange, the poor concentricity between the developing sleeve and the magnet supported by the second unit, and/or the manufacturing and assembling errors of parts, with the result that it is feared that an amount of toner (developer) transferred from the surface of the developing sleeve to the surface of the photosensitive drum is also varied, thus causing unevenness in the image density.